This invention relates to crystalline, low melting, .epsilon.-caprolactone polymers bearing basic amine functionalities which are linked to the ester chain ionically or covalently to induce catalyzed hydrolysis. The ester components can be derived from .epsilon.-caprolactone with or without small amounts of glycolide, and/or similar lactones. Such polymers with accelerated absorption profiles are especially adapted for use as transient coatings for absorbable multifilament surgical sutures (and other medical implants).
Multifilament surgical sutures such as Dexon.RTM. polyglycolide multifilament suture typically require a surface coating to improve their handling and knotting characteristics. Capitalizing on the desirable low melting temperature, crystallinity, and rheological properties of polycaprolactone and its copolymers as coating materials, several compositions based on this polymer were investigated as coatings for surgical sutures. Recognizing the fact that the .epsilon.-caprolactone homopolymer is essentially non-absorbable led to the development of copolymers of .epsilon.-caprolactone with variable amounts of more absorbable monomers to improve the coating absorbability. U.S. Pat. No. 4,624,256 discloses a suture coating copolymer of at least 90 percent .epsilon.-caprolactone and a biodegradable monomer and optionally a lubricating agent. Examples of monomers for the biodegradable polymers disclosed include glycolic acid and glycolide, as well as well-known monomers typically used to prepare absorbable polymer fibers or coatings for multifilament sutures. U.S. Pat. No. 4,788,979 and U.S. Pat. No. 4,791,929 disclose a bioabsorbable coating of a copolymer of at least 50 percent .epsilon.-caprolactone and glycolide. Sutures coated with such polymers are reported to be less stiff than sutures coated with other materials and the physical properties of the coated suture are also reported to be acceptable. U.S. Pat. No. 4,994,074 discloses copolymers of a predominant amount of .epsilon.-caprolactone, the balance being glycolide and glycolic acid. The use of glycolic acid as a comonomer into the copolymers of this invention was reported to increase the rate of absorption of the copolymer when used as a coating for multifilament surgical sutures.
Unfortunately, the problem of adequate bioabsorbability of .epsilon.-caprolactone-based polymers without detrimental effects on their desirable properties as coatings still remains. Specifically, the use of sufficient amounts of glycolide to achieve sufficient absorbability of the copolymeric coating can compromise its crystallinity and melting characteristics, for it may become amorphous or liquid near room temperature. On the other hand, the strategy of using glycolic acid to achieve the reported results in coating absorbability does limit the ability to produce sufficiently long chain molecules to achieve optimum frictional properties, due to glycolic acid's known properties as both a ring-opening initiator chain terminator. Thus, a totally new approach to modifying the absorbability of polycaprolactone and its copolymers without affecting their desirable properties as suture coatings (or coatings for surgical device) would be a more desirable goal.